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United States Patent |
5,547,790
|
Umeda
,   et al.
|
August 20, 1996
|
Electrophotographic photoconductor containing polymeric charge
transporting material in charge generating and transporting layers
Abstract
An electrophotographic photoconductor including an electroconductive
support and a photoconductive layer formed thereon, which has at least a
charge generation layer containing a charge generating material and a
polymeric charge transporting material, and a charge transport layer
containing a polymeric charge transporting material.
Inventors:
|
Umeda; Minoru (Numazu, JP);
Niimi; Tatsuya (Numazu, JP)
|
Assignee:
|
Ricoh Company, Ltd. (Tokyo, JP)
|
Appl. No.:
|
326700 |
Filed:
|
October 20, 1994 |
Foreign Application Priority Data
Current U.S. Class: |
430/58.2; 430/58.45 |
Intern'l Class: |
G03G 005/047 |
Field of Search: |
430/58,59
|
References Cited
U.S. Patent Documents
4743523 | May., 1988 | Yamashita et al. | 430/58.
|
5028687 | Jul., 1991 | Yanus et al. | 528/203.
|
5066796 | Nov., 1991 | Law | 430/78.
|
5310613 | May., 1994 | Pai et al. | 430/59.
|
5316880 | May., 1994 | Pai et al. | 430/59.
|
5342719 | Aug., 1994 | Pai et al. | 430/59.
|
Primary Examiner: Rodee; Christopher D.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier, & Neustadt, P.C.
Claims
What is claimed is:
1. An electrophotographic photoconductor comprising an electroconductive
support and a photoconductive layer formed thereon, which comprises at
least a charge generation layer comprising a charge generating material
selected from the group consisting of azo pigments, perinone pigments and
squaraines, and a polymeric charge transporting material, and a charge
transport layer comprising a polymeric charge transporting material,
wherein said polymeric charge transporting material in said charge
generation layer is selected from the group consisting of polysilylene, a
polymer having a hydrazone structure on the main chain and/or side chain
thereof, and a polymer having a tertiary amine structure on the main chain
and/or side chain thereof, and
said polymeric charge transporting material in said charge transport layer
is selected from the group consisting of polysilylene, a polymer having a
hydrazone structure on the main chain and/or side chain thereof, and a
polymer having a tertiary amine structure on the main chain and/or side
chain thereof.
2. The electrophotographic photoconductor as claimed in claim 1, wherein
said polymeric charge transporting material for use in said charge
generation layer is polysilylene.
3. The electrophotographic photoconductor as claimed in claim 1, wherein
said polymeric charge transporting material for use in said charge
generation layer is a polymer having a hydrazone structure on the main
chain and/or side chain thereof.
4. The electrophotographic photoconductor as claimed in claim 1, wherein
said polymeric charge transporting material for use in said charge
generation layer is a polymer having a tertiary amine structure on the
main chain and/or side chain thereof.
5. The electrophotographic photoconductor as claimed in claim 1, wherein
said charge generating material for use in said charge generation layer is
said azo pigment.
6. The electrophotographic photoconductor as claimed in claim 5, wherein
said polymeric charge transporting material in said charge generation
layer is polysilylene.
7. The electrophotographic photoconductor as claimed in claim 5, wherein
said polymeric charge transporting material in said charge generation
layer is a polymer having a hydrazone structure on the main chain and/or
side chain thereof.
8. The electrophotographic photoconductor as claimed in claim 5, wherein
said polymeric charge transporting material in said charge generation
layer is a polymer having a tertiary amine structure on the main chain
and/or side chain thereof.
9. The electrophotographic photoconductor as claimed in claim 1, wherein
said polymeric charge transporting material in said charge generation
layer is a polymer having a weight-average molecular weight of 1,000 to
2,000,000.
10. The electrophotographic photoconductor as claimed in claim 9, wherein
the weight-average molecular weight of said polymeric charge transporting
material in said charge generation layer is 10,000 to 1,000,000.
11. The electrophotographic photoconductor as claimed in claim 10, wherein
the polymeric charge transporting material in said charge transport layer
is the same as the polymeric charge transporting material in said charge
generation layer.
12. The electrophotographic photoconductor as claimed in claim 9, wherein
the polymeric charge transporting material in said charge transport layer
is the same as the polymeric charge transporting material in said charge
generation layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoconductor used
in a copying machine, a laser printer and a laser facsimile apparatus, and
more particularly to an electrophotographic photoconductor comprising a
charge transport layer which comprises a polymeric charge transporting
material.
2. Discussion of Background
The Carlson process and other processes obtained by modifying the Carlson
process are conventionally known as the electrophotographic methods, and
widely utilized in the copying machine and printer. In a photoconductor
for use with the electrophotographic method, an organic photoconductive
material is now widely used because such a photoconductor can be
manufactured at low cost by mass production, and causes no environmental
pollution.
Many kinds of organic photoconductors are conventionally proposed, for
example, a photoconductor employing a photoconductive resin such as
polyvinyl carbazole (PVK); a photoconductor comprising a charge transport
complex of polyvinyl carbazole (PVK) and 2,4,7-trinitrofluorenone (TNF); a
photoconductor of a pigment dispersed type in which a phthalocyanine
pigment is dispersed in a binder resin; and a function-separating
photoconductor comprising a charge generating material and a charge
transporting material. In particular, the function separating
photoconductor has now attracted considerable attention.
When the function separating photoconductor is charged to a predetermined
polarity and exposed to light, the light pass through a transparent charge
transport layer, and is absorbed by a charge generating material in a
charge generation layer. The charge generating material generates charge
carriers by the absorption of light. The charge carriers generated in the
charge generation layer are injected into the charge transport layer, and
move in the charge transport layer depending on the electrical field
generated by the charging process. Thus, latent electrostatic images are
formed on the surface of the photoconductor by neutralizing the charge
thereon. As is known, it is effective that the function separating
electrophotographic photoconductor employ in combination a charge
transporting material having an absorption intensity mainly in the
ultraviolet region, and a charge generating material having an absorption
intensity in a range from the visible region extending to the near
infrared region.
Many low-molecular weight compounds have been developed to obtain the
charge transporting materials. However, it is necessary that the
low-molecular weight charge transporting material be dispersed and mixed
with an inert polymer to prepare a coating liquid for a charge transport
layer because the film-forming properties of such a low-molecular weight
compound is very poor. The charge transport layer thus prepared by using
the low-molecular weight compound and the inert polymer is generally so
soft, that peeling of the charge transport layer easily occurs during the
repeated electrophotographic operations by the Carlson process.
In addition, the charge mobility has its limit in the above-mentioned
charge transport layer employing the low-molecular weight charge
transporting material. The Carlson process cannot be carried out at a high
speed, and the size of apparatus cannot be decreased due to the poor
charge mobility in the charge transport layer when the amount of the
low-molecular weight charge transporting material is 50 wt. % or less to
the weight of the charge transport layer. Although the charge mobility can
be improved by increasing the amount of the charge transporting material,
the film-forming properties deteriorate.
To solve the problems of the low-molecular weight charge transporting
material, considerable attention has been paid to a high-molecular weight
charge transporting material. For example, a variety of high-molecular
weight charge transporting materials are proposed as disclosed in Japanese
Laid-Open Patent Applications Nos. 50-82056, 51-73888, 54-8527, 54-11737,
56-150749, 57-78402, 63-285552, 1-1728, 1-19049 and 3-50555.
However, photosensitivity of the function-separating laminated
photoconductor in which a charge transport layer comprises a
high-molecular weight charge transporting material is extraordinarily
inferior to that of the above-mentioned laminated photoconductor employing
a low-molecular weight charge transporting material in the charge
transport layer.
To improve the photosensitivity of a laminated electrophotographic
photoconductor in which a high-molecular weight charge transporting
material is employed in the charge transport layer, it is proposed to add
a low-molecular weight charge transporting material to the charge
generation layer or the charge transport layer, as disclosed in Japanese
Laid-Open Patent Application 5-34938. However, when the low-molecular
weight charge transporting material is added to the high-molecular weight
charge transporting material in the charge transport layer, the peeling of
the charge transport layer easily occurs during the repeated operations.
0n the other hand, when the low-molecular weight charge transporting
material is contained in the charge generation layer, the photosensitivity
slightly increases, but does not attain to a satisfactory level.
As previously explained, when the charge transport layer of the function
separating laminated photoconductor comprises the low-molecular weight
charge transporting material and the inert polymer, the charge mobility,
that is, the response speed has the limitation, and the charge transport
layer easily tends to peel during the repeated operations.
The laminated photoconductor in which the high-molecular weight charge
transporting material is employed in the charge transport layer can solve
the above-mentioned problems, but causes a fatal problem of low
photosensitivity. All the characteristics cannot be satisfied as mentioned
above even though the high-molecular weight charge transporting material
is used in combination with the low-molecular weight charge transporting
material.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide an
electrophotographic photoconductor with high photosensitivity.
A second object of the present invention is to provide an
electrophotographic photoconductor capable of attaining a quick
photoresponse performance.
A third object of the present invention is to provide an
electrophotographic photoconductor showing excellent abrasion resistance
during the repeated operations.
The above-mentioned objects of the present invention can be achieved by an
electrophotographic photoconductor comprising an electroconductive support
and a photoconductive layer formed thereon, which comprises at least a
charge generation layer comprising a charge generating material and a
polymeric charge transporting material, and a charge transport layer
comprising a polymeric charge transporting material.
In the first mentioned electrophotographic photoconductor, the polymeric
charge transporting material for use in the charge generation layer may be
selected from the group consisting of polysilylene, a polymer having a
hydrazone structure on the main chain and/or side chain thereof, and a
polymer having a tertiary amine structure on the main chain and/or side
chain thereof.
In the first mentioned electrophotographic photoconductor, the charge
generating material for use in the charge generation layer may be an
organic material.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant
advantages thereof will be readily obtained as the same becomes better
understood by reference to the following detailed description when
considered in connection with the accompanying drawings, wherein:
FIG. 1 is a schematic cross-sectional view which shows one embodiment of an
electrophotographic photoconductor according to the present invention; and
FIG. 2 is a schematic cross-sectional view which shows another embodiment
of an electrophotographic photoconductor according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It is considered that photocarriers are generated when the charge
generating material is subjected to the light excitation in the charge
generation layer.
The inventors of the present invention have conducted a study of the
generation of photocarriers in the laminated photoconductor in which a
bisazo pigment and a trisazo pigment are contained in a charge generation
layer. As a result, it is found that exciton is generated in the charge
generation layer after absorption of light, and the exciton causes
dissociation at the interface between the charge generation layer and the
charge transport layer, thereby generating photocarrier. Such a discovery
is reported in the Japanese Journal of Applied Physics Vol. 29, No. 12,
pp. 2746-2750, and the Japanese Journal of Applied Physics Vol. 72, No. 1,
pp. 117-123.
After further intensive study, the inventors of the present invention have
come to the following conclusions
(1) All the organic charge generating materials can contribute to the
generation of photocarrier at the interface between the charge generation
layer and the charge transport layer.
(2) In the case where a low-molecular weight charge transporting material
is employed, a large quantity of photocarriers are generated when a charge
generating material is well mixed with the low-molecular weight charge
transporting material, and brought into contact with the low-molecular
weight charge transporting material.
(3) The photocarrier can also be generated by the contact of a charge
generating material and a high-molecular weight charge transporting
material. A large quantity of photocarriers are generated when the charge
generating material is well mixed with the high-molecular weight charge
transporting material, and brought into contact with the high-molecular
weight charge transporting material.
(4) The low-molecular weight charge transporting material contained in the
charge transport layer permeates through the charge generation layer in
the case where the charge transport layer is formed by the conventional
casting method. Therefore, the low-molecular weight charge transporting
material can be sufficiently brought into contact with the charge
generating material. In contrast to this, the high-molecular weight charge
transporting material cannot permeate through the charge generation layer,
so that the contact with the charge generating material becomes
insufficient. Consequently, the amount of generated photocarriers is
small, which causes the low photosensitivity.
On the basis of the above-mentioned study, the inventors of the present
invention have succeeded in the improvement of photosensitivity of a
laminated photoconductor comprising the high-molecular weight charge
transporting material without using any low-molecular weight charge
transporting material.
More specifically, an electrophotographic photoconductor according to the
present invention comprises an electroconductive support and a
photoconductive layer formed thereon, which comprises at least a charge
generation layer comprising a charge generating material and a polymeric
charge transporting material, and a charge transport layer comprising a
polymeric charge transporting material.
When the polymeric charge transporting material is used in the charge
transport layer, the polymeric charge transporting material cannot
permeate through the charge generation layer when the charge transport
layer is provided by the casting method. This is because the diffusion
constant of the polymeric charge transporting material is small due to its
large molecular weight. Therefore, the charge generating material comes
into contact with the polymeric charge transporting material only at the
interface between the charge generation layer and the charge transport
layer. As a result, the site where the photocarrier can be generated
(hereinafter referred to as the carrier generation site) is restricted.
According to the present invention, the carrier generation sites can
adequately be ensured in the charge generation layer because a polymeric
charge transporting material is previously added to the charge generation
layer. Although the charge transport layer comprising a polymeric charge
transporting material is provided, ample carrier generation sites can be
retained. Therefore, high photosensitivity can be obtained.
In particular, the photocarriers can be generated between the charge
generating material and the polymeric charge transporting material in a
better condition in the charge generation layer and the photosensitivity
of the photoconductor is further increased when the specific polymeric
charge transporting materials to be described later are employed, and the
charge generating material for use in the charge generation layer is an
organic material.
In addition, since the charge transport layer of the photoconductor
according to the present invention comprises a polymeric charge
transporting material, the charge mobility can be increased due to a high
density of charge transporting sites in the charge transport layer.
Accordingly, the photoconductor of the present invention is provided with
high-speed photoresponse performance, which has never been achieved in the
conventional charge transport layer comprising a low-molecular weight
charge transporting material and an inert polymer.
Furthermore, the hardness of the charge transport layer for use in the
present invention is improved because only polymeric materials are
contained therein. The peeling of the charge transport layer can be
prevented even though the photoconductor is repeatedly used for a long
period of time.
The structure of the electrophotographic photoconductor according to the
present invention will now be explained in detail by referring to FIGS. 1
and 2.
FIGS. 1 and 2 are schematic cross-sectional views which show the
embodiments of an electrophotographic photoconductor according to the
present invention. As shown in FIGS. 1 and 2, a photoconductive layer
comprising a charge generation layer 13 which comprises a charge
generating material and a polymeric charge transporting material, and a
charge transport layer 15 which comprises a polymeric charge transporting
material is overlaid on an electroconductive support 11.
The laminating order of the charge generation layer 13 and the charge
transport layer 15 is reversed in a photoconductor shown in FIG. 2 as
compared with the photoconductor shown in FIG. 1.
The electroconductive support 11 of the photoconductor according to the
present invention may exhibit electroconductive properties, and have a
volume resistivity of 10.sup.10 .OMEGA..multidot.cm or less. The
electroconductive support 11 can be prepared by coating a plastic film or
a sheet of paper, which may be in the cylindrical form, with metals such
as aluminum, nickel, chromium, nichrome, copper, silver, gold and
platinum, or metallic oxides such as tin oxide and indium oxide by the
vacuum deposition or sputtering method. Alternatively, a sheet of
aluminum, aluminum alloys, nickel, or stainless steel may be formed into a
tube by the drawing end ironing (D.I.) method, the impact ironing (I.I.)
method, the extrusion method or the pultrusion method. Subsequently, the
tube thus obtained may be subjected to surface treatment such as machining
or abrasion to prepare the electroconductive support 11 for use in the
photoconductor of the present invention.
The charge generation layer 13 comprises as the main components the charge
generating material and polymeric charge transporting material.
Specific examples of the charge generating material include organic
materials such es monoazo pigment, disazo pigment, trisazo pigment,
perylene pigment, perinone pigment, quinacridone pigment, quinone
condensation polycyclic compound, squaraines, phthalocyanine pigment,
naphthalocyanine pigment, and azulenium salt dye; and inorganic materials
such as selenium, selenium-tellurium, selenium-arsenic compound, and
a-silicon (amorphous silicon).
Particularly, the above-mentioned organic materials such as azo pigment,
perylene pigment, perinone pigment, quinacridone pigment, quinone
condensation polycyclic compound, squaraines, phthalocyanine pigment,
naphthalocyanine pigment, and azulenium salt dye can produce good results.
Of the above organic materials, the azo pigment, perylene pigment,
perinone pigment, quinacridone pigment, quinone condensation polycyclic
compound, squaraines, and azulenium salt dye are further preferable.
The above-mentioned charge generating material can be used alone or in
combination in the charge generation layer 13.
The polymeric charge traneporting material for use in the charge generation
layer 13 and the charge transport layer 15 is not particularly limited.
It is preferable that the weight-average molecular weight (Mw) of the
polymeric charge transporting material for use in the charge generation
layer 13 and the charge transport layer 15 be in the range of 1,000 to
2,000,000, and more preferably in the range of 10,000 to 1,000,000.
In particular, the following polymeric charge transporting materials are
preferably employed in the charge generation layer 13 for use in the
present invention:
(a) A polymeric material having a carbazole ring on the main chain and/or
side chain thereof.
For example, poly-N-vinylcarbazole, and compounds as disclosed in Japanese
Laid-Open Patent Applications Nos. 50-82056, 54-9632, 54-11737 and
4-183719 can be employed.
(b) A polymeric material having a hydrazone structure on the main chain
and/or side chain thereof.
For example, compounds as disclosed in Japanese Laid-Open Patent
Applications Nos. 57-78402 and 3-50555 can be employed.
(c) Polysilylene.
For example, compounds as disclosed in Japanese Laid-Open Patent
Applications Nos. 63-285552, 5-19497 and 5-70595 can be employed.
(d) A polymeric material having a tertiary amine structure on the main
chain and/or side chain thereof.
For example, N,N-bis(4-methylphenyl)-4-aminopolystyrene, and compounds as
disclosed in Japanese Laid-Open Patent Applications Nos. 1-13061, 1-19049,
1-1728, 1-105260, 2-167335, 5-66598 and 5-40350 can be employed.
(e) Other polymeric materials.
For example, formaldehyde condensation polymer of nitropylene, and
compounds as disclosed in Japanese Laid-Open Patent Applications Nos.
51-73888 and 56-150749 can be employed.
The polymeric charge transporting material for use in the charge generation
layer 13 is not limited to the above-mentioned materials. For instance, a
copolymer consisting of conventional monomers, a block polymer, a graft
polymer, a star shaped polymer, and a crosslinked polymer having an
electron donor group as disclosed in Japanese Laid-Open Patent Application
3-109406 can also be employed.
To obtain good results in the present invention, the above-mentioned
polymeric materials (b), (c) and (d) are preferably employed as the
polymeric charge transporting materials for use in the charge generation
layer 13.
To improve the photosensitivity of the photoconductor, it is preferable
that the ionization potential (I.sub.P) of the polymeric charge
transporting material for use in the charge generation layer 13 and the
ionization potential (I.sub.p ') of the charge generating material satisfy
the relationship of (I.sub.P)<(I.sub.P ')+0.2 eV.
It is preferable that the polymeric charge transporting material be
contained in the charge generation layer 13 in an amount of 0.1 to 10
parts by weight, more preferably 0.2 to 5 parts by weight, to one part by
weight of the charge generating material.
The charge generation layer 13 may further comprise an electrically inert
binder resin when necessary.
Examples of such a binder resin for use in the charge generation layer 13
are polyamide, polyurethane, polyester, epoxy resin, polyketone,
polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl
formal, polyvinyl ketone, polystyrene and polyacrylamide.
To prepare the charge generation layer 13, the charge generating material
and the polymeric charge transporting material are dispersed in a proper
solvent such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone or
dichloroethane in a ball mill, an attritor or a sand mill. The dispersion
thus obtained may appropriately be diluted to prepare a coating liquid for
the charge generation layer 13. The coating liquid for the charge
generation layer 13 is applied to the electroconductive support 11 in FIG.
1, or to the charge transport layer 15 in FIG. 2, by dip coating, spray
coating or beads coating.
Alternatively, a dispersion of the charge generating material and a
solution of the polymeric charge transporting material are separately
prepared and coated by spray coating. The dispersion of the charge
generating material and the solution of the polymeric charge transporting
material may be mixed together and the thus obtained mixture may be
subjected to spray coating.
It is preferable that the thickness of the charge generation layer 13 be in
the range of about 0.01 to 5 .mu.m, more preferably in the range of 0.1 to
2 .mu.m.
The charge transport layer 15 comprises the polymeric charge transporting
material. When the charge transport layer 15 is provided, the polymeric
charge transporting material is dissolved or dispersed in a proper solvent
such as tetrahydrofuran, dioxane, toluene, monochlorobenzene,
dichloroethane, methylene chloride or cyclohexanone to prepare a coating
liquid for the charge transport layer 15. The thus prepared coating liquid
for the charge transport layer 15 may be coated on the electroconductive
support 11 or the charge generation layer 13, and dried.
For the polymeric charge transporting material for use in the charge
transport layer 15, many conventional materials including the previously
mentioned polymeric charge transporting materials for use in the charge
generation layer 13 can be employed. The molecular weight of the polymerlc
charge transporting material for use in the charge transport layer 15 is
substantially determined by the solubility in the solvent to be employed,
or the solution viscosity at the predetermined molecular weight.
To improve the photosensitivity of the photoconductor, it is preferable
that the ionization potential (I.sub.P ") of the polymeric charge
transporting material for use in the charge transport layer 15 and the
ionization potential (I.sub.P) of the polymeric charge transporting
material for use in the charge generation layer 13 satisfy the
relationship of (I.sub.P ")<(I.sub.P)+0.2 eV.
The charge transport layer 15 may further comprise a binder resin, a
plasticizer, and a leveling agent.
Examples of the binder resin for use in the charge transport layer 15 are
thermoplastic resins and thermosetting resins such as polystyrene,
styrene-acrylonitrile copolymer, stytens-butadiene copolymer,
styrene--maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl
chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinylidene
chloride, polyerylate resin, phenoxy resin, polycarbonate, cellulose
acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal,
polyvinyl toluene, acrylic resin, silicone resin, epoxy resin, melamine
resin, urethane resin, phenolic resin and alkyd resin.
It is preferable that the amount of the binder resin be in the range of 0
to 100 parts by weight to 100 parts by weight of the polymeric charge
transporting material in the charge transport layer 15.
Any plasticizers used for general resins, such as dibutyl phthalate and
dioctyl phthalate, may be contained in the charge transport layer 15. Such
a plaeticizer may be contained in the charge transport layer in an amount
of about 0 to 30 wt. % of the total weight of the polymeric charge
transporting material.
Silicone oils such as dimethyl silicone oil and methylphenyl silicone oil,
and polymers and elisomers having a perfluoroalkyl group on the side chain
thereof can be used as the leveling agents in the charge transport layer
15. Such a leveling agent may be contained in the charge transport layer
in an amount of about 0 to 1 wt. % of the total weight of the polymeric
charge transporting material.
It is preferable that the thickness of the charge transport layer 15 be in
the range of about 5 to 100 .mu.m.
In the electrophotographic photoconductor of the present invention, an
undercoat layer may be provided between the electroconductive support 11
and the photoconductive layer. The undercoat layer for use in the present
invention comprises a resin as the main component. A resin with high
resistance to generally used organic solvents is preferably employed
because the photoconductive layer is provided on the undercoat layer using
a solvent. Examples of such a resin for use in the undercoat layer include
water-soluble resins such as polyvinyl alcohol, casein and sodium
polyacrylate; alcohol-soluble resins such as copolymer nylon and
methoxymethylated nylon; and cured resins with three dimensional network
structure such as polyurethane, melamine resin, phenolic resin,
alkyd-melamine resin and epoxy resin.
In addition, finely-divided pigment particles of metallic oxides such as
titanium oxide, silica, alumina, zirconium oxide, tin oxide and indium
oxide may be contained in the undercoat layer to prevent the appearance of
moire and to reduce the residual potential. In this case, the undercoat
layer can also be provided on the electroconductive support 11 using an
appropriate solvent in accordance with the proper coating method as
previously explained in the formation of the photoconductive layer.
The undercoat layer for use in the present invention may further comprise a
coupling agent such as silane coupling agent, titanium coupling agent or
chromium coupling agent.
Furthermore, to prepare the undercoat layer, Al.sub.2 O.sub.3 may be
deposited on the electroconductive support 11 by the anodizing process, or
an organic material such as poly-para-xylylene (parylene), or inorganic
materials such as SiO, SnO.sub.2, TiO.sub.2, ITO and CeO.sub.2 may be
vacuum-deposited on the electroconductive support 11.
It is preferable that the thickness of the undercoat layer be in the range
of 0 to 5 .mu.m.
In the present invention, a protective layer may be provided on the
photoconductive layer to protect the photoconductive layer.
The protective layer for use in the present invention comprises a resin.
Examples of such a resin include ABS resin, ACS resin, olefin-vinyl
monomer copolymer, chlorinated polyether, allyl resin, phenolic resin,
polyacetal, polyamide, polyamideimide, polyacrylate, polyallyl sulfone,
polybutylene, polybutylene terephthalate, polycarbonate, polyether
sulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic
resin, polymethylphene, polypropylene, polyphenylene oxide, polysulfone,
polystyrene, AS resin, butadiene-styrshe copolymer, polyurethane,
polyvinyl chloride, polyvlnylidene chloride and epoxy resin.
The protective layer may further comprise a fluorine-containing resin such
as polytetrafluoroethylene, and a silicone resin to improve the abrasion
resistance. In addition, inorganic materials such as titanium oxide, tin
oxide and potassium titanate may be dispersed in the above-mentioned
resins.
The protective layer may be provided on the photoconductive layer by the
conventional coating method. The thickness of the protective layer is
preferably in the range of about 0.5 to 10 .mu.m. Furthermore, a
vacuum-deposited thin film of i-C or a-SiC may be used as the protective
layer in the present invention.
Further, an intermediate layer may be interposed between the
photoconductive layer and the protective layer. The intermediate layer
comprises as the main component a binder resin such as polyamide,
alcohol-soluble nylon resin, water-soluble polyvinyl butyral resin,
polyvinyl butyral and polyvinyl alcohol.
The intermediate layer may also be provided by the conventional coating
method. The proper thickness of the intermediate layer is in the range of
about 0.05 to 2 .mu.m.
Furthermore, an antioxidant may be contained in the electrophotographic
photoconductor of the present invention to improve the environmental
resistance of the photoconductor, in particular, to prevent the decrease
of photosensitivity and the increase of residual potential due to
oxidation. The antioxidant may be contained in any layer as long as the
layer comprises an organic material. Particularly, when the antioxidant is
contained in the layer which comprises the charge transporting material,
good results can be obtained. Any conventional antioxidants may be used in
the present invention, and the commercially available antioxidants for use
in rubbers, plastics, and fats and oils may be employed.
In addition, an ultraviolet absorber may be contained in the
photoconductive layer and/or the protective layer to protect the
photoconductive layer when necessary.
Other features of this invention will become apparent in the course of the
following description of exemplary embodiments, which are given for
illustration of the invention and are not intended to be limiting thereof.
EXAMPLE 1
A coating liquid for a charge generation layer with a formulation (A) was
prepared:
[Formulation (A)]
__________________________________________________________________________
Parts by Weight
__________________________________________________________________________
Charge generating material
4
of the following formula:
##STR1##
Polymeric charge
3
transporting material of
the following formula:
(Mw: about 12,000)
##STR2##
Cyclohexanone 200
2-butanone 95
__________________________________________________________________________
The thus prepared charge generation layer coating liquid was coated on an
aluminum-deposited surface of a polyethylene terephthalate film serving as
an electroconductive support, and dried, so that a charge generation layer
with a thickness of 0.2 .mu.m was formed on the electroconductive support.
A coating liquid for a charge transport layer with a formulation (B) was
prepared:
[Formulation (B)]
______________________________________
Parts by Weight
______________________________________
Polymeric charge 10
transporting material of
the following formula:
(Mw: about 20,000)
##STR3##
Methylene chloride
80
______________________________________
The thus prepared charge transport layer coating liquid was coated on the
above prepared charge generation layer, and dried, so that a charge
transport layer with a thickness of 24 .mu.m was formed on the charge
generation layer.
Thus, an electrophotographic photoconductor No. 1 according to the present
invention was obtained.
EXAMPLE 2
The procedure for preparation of the electrophotographic photoconductor No.
1 in Example 1 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
1 was replaced by a polymeric charge transporting material (Mw: about
35,000) of the following formula:
##STR4##
Thus, an electrophotographic photoconductor No. 2 according to the present
invention was obtained.
EXAMPLE 3
The procedure for preparation of the electrophotographic photoconductor No.
1 in Example 1 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
1 was replaced by a polymeric charge transporting material (Mw: about
40,000) of the following formula:
##STR5##
Thus, an electrographic photoconductor No. 3 according to the present
invention was obtained.
COMPARATIVE EXAMPLE 1
The procedure for preparation of the electrophotographic photoconductor No.
1 in Example 1 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
1 was replaced by a polyvinyl butyral (Trademark "Denka Butyral #4000-1",
made by Denki Kagaku Kogyo K.K.).
Thus, a comparative electrophotographic photoconductor No. 1 was obtained.
COMPARATIVE EXAMPLE 2
The procedure for preparation of the comparative electrophotographic
photoconductor No. 1 in Comparative Example 1 was repeated except that 3
parts by weight of low-molecular weight charge transporting material of
the following formula were added to the charge generation layer coating
liquid for use in Comparative Example 1:
##STR6##
Thus, a comparative electrophotographic photoconductor No. 2 was obtained.
EXAMPLE 4
A coating liquid for a charge generation layer with a formulation (C) was
prepared:
[Formulation (C)]
__________________________________________________________________________
Parts by Weight
__________________________________________________________________________
Charge generating material
3
of the following formula:
##STR7##
Polymeric charge
4
transporting material of
the following formula:
(Mw: about 30,000)
##STR8##
Tetrahydrofuran
180
2-butanone 100
__________________________________________________________________________
The thus prepared charge generation layer coating liquid was coated on an
aluminum-deposited surface of a polyethylene terephthalate film serving as
an electroconductive support, and dried, so that a charge generation layer
with a thickness of 0.3 .mu.m was formed on the electroconductive support.
A coating liquid for a charge transport layer with a formulation (D) was
prepared:
[Formulation (D)]
______________________________________
Parts by Weight
______________________________________
Polymeric charge 10
transporting material of
the following formula:
(Mw: about 30,000)
##STR9##
Tetrahydrofuran 80
______________________________________
The thus prepared charge transport layer coating liquid was coated on the
above prepared charge generation layer, and dried, so that a charge
transpork layer with a thickness of 19 .mu.m was formed on the charge
generation layer.
Thus, an electrophotographic photoconductor No. 4 according to the present
invention was obtained.
EXAMPLE 5
The procedure for preparation of the electrophotographic photoconductor No.
4 in Example 4 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
4 was replaced by a polymeric charge transporting material (Mw: about
12,000) of the following formula:
##STR10##
Thus, an electrophotographic photoconductor No. 5 according to the present
invention was obtained.
EXAMPLE 6
The procedure for preparation of the electrophotographic photoconductor No.
4 in Example 4 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
4 was replaced by a polymeric charge transporting material (Mw: about
10,000) of the following formula:
##STR11##
Thus, an electrophotographic photoconductor No. 6 according to the present
invention was obtained.
EXAMPLE 7
The procedure for preparation of the electrophotographic photoconductor No.
4 in Example 4 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
4 was replaced by a formaldehyde condensation polymer of nitropylene.
Thus, an electrophotographic photoconductor No. 7 according to the present
invention was obtained.
COMPARATIVE EXAMPLE 3
The procedure for preparation of the electrophotographic photoconductor No.
4 in Example 4 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
4 was replaced by a phenoxy resin (Trademark "VYHH" made by Union Carbide
Japan K.K.)
Thus, a comparative electrophotographic photoconductor No. 3 was obtained.
EXAMPLE 8
A coating liquid for an undercoat layer with a formulation (E) was
prepared:
______________________________________
[Formulation (E)] Parts by Weight
______________________________________
Finely-divided particles of
15
titanium dioxide (Trademark
"Tipaque R-670", made by
Ishihara Sangyo Kainha, Ltd.
Polyvinyl butyral (Trademark
3
"S-Lec BL-1", made by Sekisui
Chemical Co., Ltd.
Epoxy resin (Trademark "Epicote
3
1001", made by Yuka Shell Epoxy K.K.)
2-butanone 150
______________________________________
The thus prepared undercoat layer coating liquid was coated on an aluminum
plate with a thickness of 0.2 mm serving as an electroconductive support,
and dried, so that an undercoat layer with a thickness of 2 .mu.mwas
formed on the electroconductive support.
A coating liquid for a charge generation layer with a formulation (F) was
prepared:
[Formulation (F)]
______________________________________
Parts by Weight
______________________________________
Charge generating material
4
of the following formula:
##STR12##
Polymeric charge 2
transporting material of
the following formula:
(Mw: about 25,000)
##STR13##
Cyclohexanone 200
Methylcyclohexanone
90
______________________________________
The thus prepared charge generation layer coating liquid was coated on the
above prepared undercoat layer, and dried, so that a charge generation
layer with a thickness of 0.2 .mu.m was formed on the undercoat layer.
A coating liquid for a charge transport layer with a formulation (G) was
prepared:
[Formulation (G)]
______________________________________
Parts by Weight
______________________________________
Polymeric charge 10
transporting material
of the following formula:
(Mw: about 50,000)
##STR14##
Methylene chloride 80
______________________________________
The thus prepared charge transport layer coating liquid was coated on the
above prepared charge generation layer, and dried, so that a charge
transport layer with a thickness of 22 .mu.m was formed on the charge
generation layer.
Thus, an electrophotographic photoconductor No. 8 according to the present
invention was obtained.
EXAMPLE 9
The procedure for preparation of the electrophotographic photoconductor No.
8 in Example 8 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
8 was replaced by a polymeric charge transporting material (Mw: about
40,000) of the following formula:
##STR15##
Thus, an electrophotographic photoconductor No. 9 according to the present
invention was obtained.
EXAMPLE 10
The procedure for preparation of the electrophotographic photoconductor No.
8 in Example 8 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
8 was replaced by a polymeric charge transporting material (Mw: about
26,000) of the following formula:
##STR16##
Thus, an electrophotographic photoconductor No. 10 according to the present
invention was obtained.
COMPARATIVE EXAMPLE 4
The procedure for preparation of the electrophotographic photoconductor No.
8 in Example 8 was repeated except that the polymeric charge transporting
material for use in the charge generation layer coating liquid in Example
8 was replaced by a polyvinyl formal (Trademark "Denka Formal #100", made
by Denki Kagaku Kogyo K.K.).
Thus, a comparative electrophotographic photoconductor No. 4 was obtained.
COMPARATIVE EXAMPLE 5
The procedure for preparation of the comparative electrophotographic
photoconductor No. 4 in Comparative Example 4 was repeated except that 2
parts by weight of a low-molecular weight charge transporting material of
the following formula were added to the charge generation layer coating
liquid for use in Comparative Example 4:
##STR17##
Thus, a comparative electrophotographic photoconductor No. 5 was obtained.
COMPARATIVE EXAMPLE 6
The procedure for preparation of the comparative electrophotographic
photoconductor No. 4 in Comparative Example 4 was repeated except that 10
parts by weight of the same low-molecular weight charge transporting
material of the following formula, as used in Comparative Example 5 were
added to the charge transport layer coating liquid for use in Comparative
Example 4:
##STR18##
Thus, a comparative electrophotographic photoconductor No. 6 was obtained.
EXAMPLE 11
A coating liquid for a charge transport layer with a formulation (H) was
prepared:
[Formulation (H)]
______________________________________
Parts by Weight
______________________________________
Polymeric charge 5
transporting material of
the following formula:
(Mw: about 40,000)
##STR19##
Polymeric charge 5
transporting material of
the following formula:
(Mw: about 60,000)
##STR20##
Toluene 80
______________________________________
The thus prepared charge transport layer coating liquid was coated on an
aluminum plate with a thickness of 0.2 mm serving as an electroconductive
support, and dried, so that a charge transport layer with a thickness of
20 .mu.m was formed on the electroconductive support.
A coating liquid for a charge generation layer with a formulation (I) was
prepared:
[Formulation (I)]
______________________________________
Parts by Weight
______________________________________
Charge generating material
3
of the following formula:
##STR21##
Polymeric charge 4
transporting material of
the following formula:
(Mw: about 40,000)
##STR22##
Cyclohexanone 200
______________________________________
The thus prepared charge generation layer coating liquid was coated on the
above prepared charge transport layer, and dried, so that a charge
generation layer with a thickness of 0.4 .mu.m was formed on the charge
transport layer.
A coating liquid for a protective layer with a formulation (J) was
prepared:
[Formulation (J)]
______________________________________
Parts by Weight
______________________________________
Antimony-oxide-containing
30
tin oxide (Amount of antimony
oxide: 10 wt. %)
Styrene - methacrylic acid -
10
N-methylolmethacrylamide resin
Toluene 80
n-butanol 70
______________________________________
The thus prepared protective layer coating liquid was coated on the above
prepared charge generation layer, and dried, so that a protective layer
with a thickness of 3 .mu.m was formed on the charge generation layer.
Thus, an electrophotographic photoconductor No. 11 according to the present
invention was obtained.
EXAMPLE 12
The procedure for preparation of the electrophotographic photoconductor No.
11 in Example 11 was repeated except that the polymeric charge
transporting material for use in the charge generation layer coating
liquid in Example 11 was replaced by a polymeric charge transporting
material (Mw: about 12,000) of the following formula:
##STR23##
Thus, an electrophotographic photoconductor No. 12 according to the present
invention was obtained.
EXAMPLE 13
The procedure for preparation of the electrophotographic photoconductor No.
11 in Example 11 was repeated except that the polymeric charge
transporting material for use in the charge generation layer coating
liquid in Example 11 was replaced by a polymeric charge transporting
material (Mw: about 8,000) of the following formula:
##STR24##
Thus, an electrophotographic photoconductor No. 13 according to the present
invention was obtained.
COMPARATIVE EXAMPLE 7
The procedure for preparation of the electrophotographic photoconductor No.
11 in Example 11 was repeated except that the polymeric charge
transporting material for use in the charge generation layer coating
liquid in Example 11 was replaced by a polysulfone (Trademark "P-1700",
made by Nissan Chemical Industries, Ltd.).
Thus, a comparative electrophotographic photoconductor No. 7 was obtained.
COMPARATIVE EXAMPLE 8
The procedure for preparation of the comparative electrophotographic
photoconductor No. 7 in Comparative Example 7 was repeated except that 3
parts by weight of a low-molecular weight charge transporting material of
the following formula were added to the charge generation layer coating
liquid for use in Comparative Example 7:
##STR25##
Thus, a comparative electrophotographic conductor No. 8 was obtained.
EXAMPLE 14
A coating liquid for an undercoat layer with a formulation (K) was
prepared:
______________________________________
[Formulation (K)] Parts by Weight
______________________________________
10% aqueous solution of
15
water-soluble polyvinyl acetal
(Trademark "W-101", made by
Sekisui Chemical Co., Ltd.)
Water 20
Methanol 50
______________________________________
The thus prepared undercoat layer coating liquid was coated on an aluminum
plate with a thickness of 0.2 mm serving as an electroconductive support,
and dried, so that an undercoat layer with a thickness of 0.3 .mu.m was
formed on the electroconductive support.
A coating liquid for a charge generation layer with a formulation (L) was
prepared:
[Formulation (L)]
______________________________________
Parts by Weight
______________________________________
Charge generating material
3
of the following formula:
##STR26##
Polymeric charge 4
transporting material of
the following formula:
(Mw: about 12,000)
##STR27##
Cyclohexanone 200
4-methyl-2-pentanone
90
______________________________________
The thus prepared charge generation layer coating liquid was coated on the
above prepared undercoat layer, and dried, so that a charge generation
layer with a thickness of 0.2 .mu.m was formed on the undercoat layer.
A coating liquid for a charge transport layer with a formulation (M) was
prepared:
[Formulation (M)]
______________________________________
Parts by Weight
______________________________________
Polycarbonate (Trademark "Panlite
6
K-1300", made by Teijin Limited.)
Polymeric charge 10
transporting material
of the following formula:
(Mw: about 7,000)
##STR28##
Tetrahydrofuran 80
______________________________________
The thus prepared charge transport layer coating liquid was coated on the
above prepared charge generation layer, and dried, so that a charge
transport layer with a thickness of 25 .mu.m was formed on the charge
generation layer.
Thus, an electrophotographic photoconductor No. 14 according to the present
invention was obtained.
EXAMPLE 15
The procedure for preparation of the electrophotographic photoconductor No.
14 in Example 14 was repeated except that the polymeric charge
transporting material for use in the charge generation layer coating
liquid in Example 14 was replaced by a polymeric charge transporting
material (Mw: about 14,000) of the following formula:
##STR29##
Thus, an electrophotographic photoconductor No. 15 according to the present
invention was obtained.
EXAMPLE 16
The procedure for preparation of the electrophotographic photoconductor No.
14 in Example 14 was repeated except that the polymeric charge
transporting material for use in the charge generation layer coating
liquid in Example 14 was replaced by a polymeric charge transporting
material (Mw: about 60,000) of the following formula:
##STR30##
Thus, an electrophotographic photoconductor No. 16 according to the present
invention was obtained.
EXAMPLE 17
The procedure for preparation of the electrophotographic photoconductor No.
14 in Example 14 was repeated except that the polymeric charge
transporting material or use in the charge generation layer coating liquid
in Example 14 was replaced by a polymeric charge transporting material
(Mw: about 19,000) of the following formula:
##STR31##
Thus, an electrophotographic photoconductor No. 17 according to the present
invention was obtained.
COMPARATIVE EXAMPLE 9
The procedure for preparation of the electrophotographic photoconductor No.
14 in Example 14 was repeated except that the polymeric charge
transporting material for use in the charge generation layer coating
liquid in Example 14 was replaced by a phenoxy resin (Trademark "VYHH",
made by Union Carbide Japan K.K.).
Thus, a comparative electrophotographic photoconductor No. 9 was obtained.
Each of the thus prepared electrophotographic photoconductors No. 1 through
No. 17 according to the present invention and comparative
electrophotographic photoconductors No. 1 through No. 9 was charged
negatively or positively in the dark under application of -5.2 kV or +5.6
kv of corona charge for 10 seconds, using a commercially available
electrostatic copying sheet testing apparatus ("Paper Analyzer Model
SP-428", made by Kawaguchi Electro Works Co., Ltd.). The surface potential
v.sub.10 (v) of each photoconductor was measured 10 seconds after the
initiation of charging. Then, each photoconductor was allowed to stand in
the dark for 10 seconds without applying any charge there=o, and the
surface potential V.sub.20 (V) was measured after the dark decay. Each
photoconductor was then illuminated by a tungsten lamp in such a manner
that the lllumtnance on the illuminated surface of the photoconductor was
5 lux, and the exposure E.sub.1/2 (lux.sec) required to reduce the surface
potential V.sub.20 (V) to 1/2 the surface potential V.sub.20 (V) was
measured. In addition, the surface potential V.sub.40 (V) of each
photoconductor wes measured after the photoconductor was exposed to the
tungsten lamp for 20 seconds.
The results are shown in TABLE 1.
TABLE 1
______________________________________
V.sub.10
V.sub.20 E.sub.1/2 V.sub.40
(V) (V) (lux .multidot. sec)
(V)
______________________________________
Ex. 1 -1307 -1002 1.08 0
Ex. 2 -1283 -928 1.11 -2
Ex. 3 -1246 -951 1.06 -1
Comp. -1415 -1174 * 625
Ex. 1
Comp. -1344 -1032 1.86 -37
Ex. 2
Ex. 4 -1187 -934 0.87 -3
Ex. 5 -1096 -915 0.85 -2
Ex. 6 -1136 -927 0.90 0
Ex. 7 -1216 -970 1.01 -15
Comp. -1289 -1064 * -524
Ex. 3
Ex. 8 -1031 -874 1.05 -2
Ex. 9 -1016 -856 1.03 0
Ex. 10 -1045 -839 1.02 15
Comp. -1172 -947 * -483
Ex. 4
Comp. -1126 -901 1.79 -29
Ex. 5
Comp. -1065 -844 1.00 -2
Ex. 6
Ex. 11 1162 907 1.22 4
Ex. 12 1104 924 1.09 2
Ex. 13 1097 911 1.15 5
Comp. 1171 982 * 517
Ex. 7
Comp. 1125 904 1.70 3
Ex. 8
Ex. 14 -1362 -1004 1.85 -7
Ex. 15 -1297 -1018 1.7 -4
Ex. 16 -i326 -996 1.71 -6
Ex. 17 -1288 -989 2.76 -31
Comp. -1385 -1050 5.76 -162
Ex. 9
______________________________________
*It was impossible to obtain the value of E.sub.1/2 because the surface
potential V.sub.20 did not reduce to 1/2 the surface potential V.sub.20
within 20 seconds of exposure.
As can be seen from the results shown in TABLE 1, the electrophotographic
photoconductors of the present invention exhibit high photosensitivity and
high-speed photoresponse performance.
Furthermore, the photoconductor No. 8 according to the present invention
and the comparative photoconductor No. 6 were subjected to the abrasion
test, using a commercially available abrasion tester "Rotary Abrasion
Tester", made by Toyo Seiki Seisaku-sho, Ltd. As a result, the abrasion
amount of the photoconductor No. 8 of the present invention was 0.02 g,
and that of the comparative photoconductor No. 6 was 0.11 g after 1,000
rotations.
It is apparent that the photoconductor of the present invention is superior
in the abrasion resistance.
As previously explained, the problem of low photosensitivity caused by the
conventional functionseparating laminated photoconductor in which a
polymeric charge transporting material is employed in the charge transport
layer can be solved by adding a polymeric charge transporting material to
the charge generation layer. According to the present invention, a
photoconductor with high photosensitivity can be provided even though the
polymeric charge transporting material is employed in the charge transport
layer.
Further, the abrasion resistance of the photoconductor according to the
present invention is excellent.
Japanese Patent Application No. 5-262409 filed on Oct. 20, 1993 is hereby
incorporated by reference.
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